Efficient Ni-N-C Gas Diffusion Electrodes for Near Neutral and Acidic CO2 Reduction in a Zero-Gap Configuration

Abstract

The electrochemical CO2 reduction can be a key technology for a fossil free future but for industrial applications it is necessary to analyse and understand the cathode. As one of the main problems is the low utilization efficiency of CO2 in AEM approaches due to the carbonate formation we have to find solutions to solve carbonate formation by maintain high selectivity.In this work we investigated NiNC cathode GDEs for CO2 reduction to CO in a zero-gap MEA cell regarding their activity in a classic AEM, BPM and CEM approach. We show that the CO2 access of the catalyst is important to achieve a high performance. In an AEM approach with near neutral conditions on the anode we can reach 85% FE towards CO at 300 mA cm-2 at 3.6 V with single pass conversion of 40% which is close to the theoretical maximum. In addition, we can report high energy efficiency but only a utilization efficiency of around 50%.Our newly introduced CCC value give information about the consumption of CO2 by the produced OH- during the CO2RR. The CCC value in combination with the selectivity enable insights in the mass transfer during the CO2 reduction in an AEM setup and give information about the accessibility of the catalyst and in addition we can monitor the flooding.On the other Hand, we show that our NiNC GDE is stable under acidic conditions in a PEM and BPM zero-gap cell. The protons help to increase the utilization efficiency as the carbonate will react back to CO2 and water. Therefore, we investigated the activity with DI water and diluted H2SO4 at the anode and the protons in the BPM approach will be generated in situ due to water dissociation. In pure water, 0.01 and 0.1M H2SO4 we can achieve a selectivity above 80% towards CO at 100 mA cm-2 with cell potentials around 3 V which are comparable to the AEM configuration with 0.1M KHCO3. If we use a BPM approach, we can even push the single pass conversion towards CO to 70% at 500 mA cm-2.The CCC value is in the perfect case 0 as we do not consume any additional CO2 but can indicating flooding as the CCC is rising. This indicates water accumulation which can hinder the neutralization of the carbonate/OH- and CO2 will be consumed and can precipitate in the flow channel. Figure 1